During fabrication of integrated circuits such as, for example, volatile or non-volatile memory devices, analog circuits or logic circuits, various semiconductor fabrication processes are applied to a semiconductor wafer. After a predetermined sequence of fabrication processes, analyzing steps are carried out to check the proper performance of the fabrication processes.
For example, after patterning processes, e.g., after development of an exposed resist layer or after a masked etch process, optical inspection methods may be performed. A high resolution camera captures images of or a laser scans sections of the wafer that may be assigned to functional devices, e.g., integrated circuits. The captured images are compared against each other or a reference image to identify deviations in the patterns that may be interpreted as defects. The identified defects are assigned to a device coordinate system identifying the corresponding device on the wafer and the position of the defect with reference to a local coordinate system referencing to the respective functional device.
The use of optical inspection tools, which are based on the comparison of images or patterns is restricted to a functional, printed area of the wafer that is accessible for lithographic tools. A narrow edge area of the wafer that extends along the outer edge of the wafer and that surrounds the functional area is typically not accessible for lithographic tools. As no or only fragmentary patterns are printed in the edge area, defects occurring there are not detectable by an optical inspection tool which is based on an image comparison of patterned sections.
A typical wafer edge defect inspection tool includes an inspection system with one or more inspection cameras or laser scanners that scan the edge area for defects on both surfaces of the wafer. For this purpose, either the wafer is fixed and the inspection system is directed along the perimeter of the wafer or the inspection system is fixed and the wafer is rotated to scroll the perimeter versus the inspection system. Typically, the position of defects detected by the edge defect inspection tool is referenced to a mark, which may be a notch or a flattened section in the perimeter of the wafer in terms, for example, of a polar coordinate system or a distance between the defect and the mark on the perimeter.
A need exists for a wafer inspection system that makes feasible a thorough defect analysis.